public class Main {
 
    public static boolean containsSubstring(String s1, String s2) {
        if(s2.length()==0 && s1!=null)
            return true;
 
        for(int i=0; i < s1.length() - s2.length() + 1; i++) {
            int k = 0;
            while (k < s2.length() && s1.charAt(k+i) == s2.charAt(k++));
            if (k == s2.length() && s1.charAt(k+i-1) == s2.charAt(k-1)) return true;
        }
        return false;
    }
 
    public static void main(String[] args) {
        System.out.println(containsSubstring("abcd", "cd"));
        System.out.println(containsSubstring("abcdabcde", "abcde"));
        System.out.println(containsSubstring("abcd", "d"));
        System.out.println(containsSubstring("abcd", "a"));
        System.out.println(containsSubstring("abddde", "ddd"));
        System.out.println(containsSubstring("abddde", "de"));
        System.out.println(containsSubstring("abddde", ""));
        System.out.println();
        System.out.println(containsSubstring("a", "de"));
        System.out.println(containsSubstring("abcde", "ed"));
        System.out.println(containsSubstring("abddde", "ddz"));
        System.out.println(containsSubstring("abddde", "bde"));
        System.out.println(containsSubstring("abddde", "dee"));
        System.out.println(containsSubstring("abddde", "ee"));
        System.out.println(containsSubstring("", "ee"));
    }
 
}

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